1. Field of the Invention
The present invention relates to a method and a device of receiving digital signals and a receiver and more particularly, to a method and a device of outputting the demodulation result in soft-decision decoding that enhances the decoding capability of error-correcting codes, which makes it possible to output necessary reliability information with high accuracy, and a receiver using the method or device.
2. Description of the Prior Art
The soft-decision decoding technique is a technique that estimates the original digital signal from a noise-containing digital signal that has been sent through transmission lines by deciding the level of the noise-containing digital signal as a multi-valued signal (not a two-valued signal) using a plurality of threshold values. In other words, this technique is one that estimates the two-valued (i.e., xe2x80x9c0xe2x80x9d and xe2x80x9c1xe2x80x9d), original information through the multi-valued decoding by deciding the level of the noise-containing digital signal using a plurality of threshold values. This technique has an advantage that the error correction rate is better than that of the hard-decision decoding technology that estimates the two-valued, original information through the two-valued decoding by deciding the level of the noise-containing digital signal using a single threshold value.
An example of the prior-art soft-decision decoding systems is shown in the Japanese Non-Examined Patent Publication No. 8-317006 published in November 1996. In this system, the level reliability information on the basis of the received signal level and the phase reliability information on the basis of the received signal phase are used as the reliability information necessary for soft decision decoding. This prior-art system is explained below with reference to FIG. 1.
As shown in FIG. 1, the prior-art soft-decision decoding system comprises an input terminal 1000, a demodulation circuit 1001, a level detection circuit 1002, a level normalization circuit 1003, a soft-decision result calculation circuit 1004, a phase-reliability detection circuit 1006, and an output terminal 1005.
A received signal RS inputted through the input terminal 1000 is applied to the demodulation circuit 1001. The circuit 1001 demodulates the signal RS to generate a demodulated signal and then, decodes the demodulated signal using the soft-decision decoding technique. Thus, the circuit 1001 outputs a decision result, i.e., the demodulated data DD, to the level normalization circuit 1003, the soft-decision result calculation circuit 1004, and the phase-reliability detection circuit 1006.
The received signal RS is further applied to the level detection circuit 1002 and the phase-reliability detection circuit 1006. The level detection circuit 1002 detects the level of the signal RS thus applied and outputs a receiving level signal RSL to the level normalization circuit 1003. The level normalization circuit 1003 normalizes the level of the receiving level signal RSL on the basis of the decision result or demodulated data DD, outputting a receiving level reliability data LR. The xe2x80x9creceiving level reliabilityxe2x80x9d means the reliability relating to the receiving level of the received signal RS. The normalization operation of the circuit 1003 is necessitated by the following reason.
Since the decision result or demodulated data DD is a multi-valued demodulated data having different levels, the receiving level reliability is unable to be correctly estimated or evaluated from the receiving level itself. In other words, the receiving level reliability needs to be normalized.
On the other hand, the phase-reliability detection circuit 1006 detects the phase difference between the received signal RS and the demodulated data or decision result DD, outputting the level-based reliability data PR to the soft-decision result calculation circuit 1004.
The soft-decision result calculation circuit 1004 receives the demodulated data DD, the phase-based reliability data PR, and the level-based reliability data LR, outputting a demodulation data DR applicable to the subsequent decoding operation.
With the prior-art soft-decision decoding system shown in FIG. 1, normalization is essential for calculating the level-based reliability data LR on the basis of the decision result or demodulated data DD, which raises a problem that the circuit scale of the system becomes large.
Also, if the decision result or demodulated data DD is incorrect due to noise, there arises a problem that the reliability of the level-based reliability data LR, which is dependent upon the decision result DD, is lowered and as a result, the decoding capability of the error-correction codes degrades.
Accordingly, an object of the present invention is to provide a method and a device of outputting a demodulation result in soft-decision decoding that make it possible to output necessary reliability information with high accuracy using a simple circuit configuration.
Another object of the present invention is to provide a receiver having an enhanced decoding capability of error-correcting codes.
The above objects together with others not specifically mentioned will become clear to those skilled in the art from the following description.
According to a first aspect of the present invention, a method of outputting a demodulation result in soft-decision decoding is provided, which is comprised of the steps of:
(a) demodulating a received signal and deciding the received signal thus demodulated using a soft decision technique, outputting a decision result;
(b) estimating a distortion of the received signal generated in a communication channel, outputting a channel distortion data; and
(c) calculating a demodulation result on the basis of the decision result and the channel distortion data.
With the method of outputting a demodulation result in soft-decision decoding according to the first aspect, the distortion of the received signal generated in the communication channel is estimated to output the channel distortion data and then, the demodulation result is calculated on the basis of the decision result and the channel distortion data. This means that the channel distortion data (instead of the level of the received signal) is used as the level reliability information. Thus, the level reliability information can be obtained independent of the decision result, which simplifies the circuit configuration.
As a result, the necessary reliability information can be outputted with high accuracy using a simple circuit configuration.
According to a second aspect of the present invention, another method of outputting a demodulation result in soft-decision decoding is provided, which is comprised of the steps of:
(a) detecting a channel distortion of a received signal generated in a communication channel using a training signal contained in the received signal and a reference training signal, outputting a channel distortion data;
(b) generating a distortion-based reliability data from the channel distortion data;
(c) compensating the received signal using the channel distortion data, generating a compensated, received signal;
(d) demodulating the compensated, received signal and deciding the received signal thus demodulated using a soft decision technique, outputting a decision result; and
(e) outputting a demodulation result using the decision result and the distortion-based reliability data.
With the method of outputting a demodulation result in soft-decision decoding according to the second aspect, the channel distortion of the received signal generated in the communication channel is detected using the training signal contained in the received signal and the reference training signal. Also, the distortion-based reliability data is generated from the channel distortion data of the received signal. The received signal is compensated using the channel distortion data to thereby generate the compensated, received signal. Using the compensated, received signal, the decision result is generated. Thus, the channel distortion data (instead of the level of the received signal) of the received signal is used as the level reliability information.
As a result, the level reliability information can be obtained independent of the decision result and therefore, the necessary reliability information can be outputted with high accuracy using a simple circuit configuration.
According to a third aspect of the present invention, a device of outputting a demodulation result in soft-decision decoding is provided, which is comprised of:
(a) a demodulator means for demodulating a received signal and for deciding the received signal thus demodulated using a soft decision technique, outputting a decision result;
(b) a channel distortion estimator means for estimating a distortion of the received signal generated in a communication channel, outputting a channel distortion data to the demodulator means; and
(c) a demodulation result calculator means for calculating a demodulation result on the basis of the decision result from the demodulator means and the channel distortion data from the channel distortion estimator means.
With the device of outputting a demodulation result in soft-decision decoding according to the third aspect, because of the same reason as that of the method according to the first aspect, the necessary reliability information can be outputted with high accuracy using a simple circuit configuration.
According to a fourth aspect of the present invention, another device of outputting a demodulation result in soft-decision decoding is provided, which is comprised of:
(a) a channel distortion detector means for detecting a channel distortion of a received signal generated in a communication channel using a training signal contained in the received signal and a reference training signal, outputting a channel distortion data;
(b) a distortion-based reliability data generator means for generating a distortion-based reliability data from the channel distortion data;
(c) a compensator means for compensating the received signal using the channel distortion data, generating a compensated, received signal;
(d) a demodulator means for demodulating the compensated, received signal and deciding the received signal thus demodulated using a soft decision technique, outputting a decision result; and
(e) a demodulation result output means for outputting a demodulation result using the decision result and the distortion-based reliability data.
With the device of outputting a demodulation result in soft-decision decoding according to the fourth aspect, because of the same reason as that of the method according to the second aspect, the necessary reliability information can be outputted with high accuracy using a simple circuit configuration.
According to a fifth aspect of the present invention, a receiver is provided, which is comprised of:
(a) a demodulation circuit for outputting n decision results corresponding to n frequency-multiplexed sub-carriers of a received signal by demodulating the n sub-carriers and deciding then sub-carriers thus demodulated using a soft decision technique, where n is an integer greater than unity;
the n decision results being generated by using n channel-distortion coefficients corresponding to the n sub-carriers;
(b) a channel-distortion calculation circuit for calculating the n channel-distortion coefficients corresponding to the n sub-carriers;
(c) a reliability information calculation circuit for calculating reliability information for the n decision results corresponding to the n sub-carriers using the n channel-distortion coefficients; and
(d) a demodulation result output circuit for outputting a demodulation result using the n decision results corresponding to then sub-carriers and the reliability information corresponding to the n sub-carriers.
With the receiver according to the fifth aspect, because of substantially the same reason as that of the method according to the first aspect, an enhanced decoding capability of error-correcting codes can be realized.
In a preferred embodiment of the receiver according to the fifth aspect of the invention, the channel-distortion circuit comprises;
a training signal point memory for storing training signal points corresponding to n reference training signal points corresponding to the n sub-carriers; and
n division circuits for respectively dividing n training signal points of the n sub-carriers by the n reference training signal points to thereby output the n channel-distortion coefficients.
In another preferred embodiment of the receiver according to the fifth aspect of the invention, the reliability information calculator circuit comprises;
n level detection circuits for detecting the level of the n channel-distortion coefficients;
a threshold memory for storing threshold values for quantizing the reliability with respect to the level of the n channel-distortion coefficients; and
n quantization circuits for quantizing outputs of the n level detection circuits using the threshold values, thereby outputting reliability information corresponding to then decision results.
In still another preferred embodiment of the receiver according to the fifth aspect of the invention, the demodulation circuit outputs the n decision results corresponding to the n sub-carriers and n pieces of distance reliability information as reliability information for the n decision results.
In a further preferred embodiment of the receiver according to the fifth aspect of the invention, the demodulation circuit comprises;
n multiplier circuits for multiplying the n sub-carriers by the corresponding n channel-distortion coefficients;
n decision circuits for outputting the n decision results by demodulating the n sub-carriers and outputs of the n multiplier circuits;
n distance calculation circuits for calculating a distance between the n decision results and the outputs of the n multiplier circuits in a signal space;
a threshold memory for storing threshold values for quantizing the outputs of the n distance calculation circuits; and
n quantization circuits for quantizing the outputs of the n distance calculator circuits using the threshold values stored in the threshold memory and the outputs of then distance calculator circuits, thereby outputting distance reliability information as the reliability information for the n decision results.